162 Avierican Seashells 



I to 1/4 inches in length, rather slender, with a quite deep suture, thus 

 giving the whorls a shouldered appearance. No umbilicus. Color a uniform, 

 chalky grayish white. Outer lip with a thickened varix. Whorls with numer- 

 ous groups of foliated costae. Surface pitted with small holes when the 

 costae or ribs are closely crowded. Uncommon from i8 to 75 fathoms. 

 C. arcella Rehder is believed to be the young of this species. 



Genus Actrsa Morch 1857 



Acirsa costulata Mighels and Adams Costate Wentletrap 



Arctic Ocean to Massachusetts. 



% to 1% inches in length, rather turreted in shape and fairly thin in 

 structure. 8 to 9 moderately convex whorls are devoid of sculpture except 

 for weak, incised spiral lines and, in the early whorls, numerous but incon- 

 spicuous costae. Color straw to whitish, rarely with brown lines. Uncom- 

 mon from low water to 50 fathoms. This is Scalaria borealis Beck. 



Genus Opalia H. and A. Adams 1853 

 Subgenus Demise ala de Boury 1886 



Opalia hotessieriana Orbigny Hotessier's Wentletrap 



Plate 2 2g 



Southeast Florida and the Caribbean. 



H to /4 inch in length, moderately slender. Characterized by 10 to 14 

 large, square notches along the suture of each whorl. Ribs are rather weak. 

 Surface, in fresh specimens, microscopically pitted. Color grayish white. 

 Not uncommon from low water to 90 fathoms. O. crenata Linne (same 

 range, but also the Eastern Atlantic) is larger, its whorls more strongly 

 shouldered, and the notches at the suture are much weaker and more nu- 

 merous. 



Opalia UDrobleiDskii Morch Wroblewski's Wentletrap 



Plate 20) 



Forrester Island, Alaska, to off San Diego. 



I to I M inches in length, slender, heavy; looks beachworn; grayish white 

 in color, often stained purple from the animal's dye gland. With 6 to 8 low, 

 pronounced, axial, wide ribs. Base of shell bounded by a strong, smooth, 

 low, spiral cord. Fairly common. O. chacei (Chace's Wentletrap) is probably 

 a southern representative of this species. 



Opalia insculpta Carpenter Scallop-edged Wentletrap 



Southern California to west Mexico. 



